Feedforward/feedback litho process control of stress and overlay

ABSTRACT

A method and apparatus for process control in a lithographic process are described. Metrology may be performed on a substrate either before or after performing a patterning process on the substrate. One or more correctables to the lithographic patterning process may be generated based on the metrology. The patterning process performed on the substrate (or a subsequent substrate) may be adjusted with the correctables.

CLAIM OF PRIORITY

This application claims the benefit of priority of commonly-assignedco-pending U.S. Provisional Patent Application No. 60/940,953, filed May30, 2007, the entire contents of which are incorporated herein byreference.

This application is a continuation of and claims the benefit of priorityof commonly-assigned co-pending U.S. patent application Ser. No.12/130,699, filed May 30, 2008, the entire contents of which areincorporated herein by reference.

FIELD OF THE INVENTION

This invention generally relates to substrate processing and moreparticularly to process control in a lithographic process.

BACKGROUND OF THE INVENTION

Various methods of measuring the stress in films deposited onsemiconductor wafers are known in the art. Most commonly, themeasurement is performed by measuring the shape of the wafer before aprocess step and then repeating the shape measurement after the processstep. The stress of a film deposited (or removed) during the processstep is calculated from the change in shape of the wafer and the knownelastic modulus of the semiconductor material comprising the bulk of thewafer. The thickness of the wafer and/or film may be known prior to theshape measurement, or may be measured by the same apparatus making theshape measurement. If the stress and film thickness are reasonablyuniform across the wafer and if the change in shape of the wafer is notlarge compared with the thickness of the wafer (all of which conditionsare usually satisfied by most semiconductor manufacturing processsteps), then Stoney's equation (G. G. Stoney (1909) Proc. Roy. Soc. A82,172) may be used to calculate the film stress from the change in wafercurvature deduced from the change in wafer shape.

U.S. Pat. Nos. 5,134,303 and 5,248,889 (Blech et al) disclose atechnique for scanning laser beams along a diameter of a wafer in orderto measure the slope, and hence, curvature of the wafer. It will beunderstood by those of ordinary skill in the art that either the beammay be scanned across the wafer or the wafer may be moved under the beamin order to perform the measurement. If the stress of the film isuniform, measurement of a single diameter usually suffices. If thestress of the film is non-uniform, measurement of multiple diameters isoften needed to build up a more complete picture of the wafer curvature.

U.S. Pat. No. 5,912,738 to Chason et al. describes a technique that usesmultiple laser beams to make simultaneous measurements of slope atmultiple locations on a wafer, thus speeding up the measurement byreducing, or eliminating, the need for relative scanning of the beam andwafer.

U.S. Pat. No. 6,031,611 to Rostakis et al. describes a technique that iscapable of measuring slope (in one direction) simultaneously at manypoints across the whole surface of a wafer. A second measurement can bemade with the wafer rotated by 90° in order to measure the other tiltcomponent if that is also desired.

As an alternative to measuring the tilt of the wafer, it is alsopossible to measure the displacement of the wafer as a function ofposition across the wafer. U.S. Pat. No. 4,750,141 to Judell et al.discloses such a technique. The displacement measurement may be donewith capacitive sensors (as disclosed in '141) or by optical or othermeans. U.S. Pat. No. 6,100,977 to Muller and U.S. Pat. No. 6,847,458 toFreischlad et al. disclose techniques that are capable of essentiallysimultaneously measuring the displacement of both sides of the of waferusing optical interferometers.

Other methods of measuring stress are known in the art. These othermethods are generally less convenient for use in a productionenvironment than the change in wafer shape metrology just describedbecause these other techniques are generally slower or require moreexpensive hardware.

High resolution X-ray diffraction can measure the strain of the latticeof the semiconductor comprising the bulk of the wafer (see, for example,“High Resolution X-ray Diffractometerty and Topography” D. K. Bowen, B.K. Tanner (1998), CRC Press ISBN 0-8506-6758-5), Chapter 1, pp. 1-13,which is incorporated herein by reference. Since the elastic propertiesof common semiconductor materials are well known, a measurement ofstrain can be used to compute stress. Since the measurement of latticeconstants depends only on the knowledge of the wavelength of the X-raysand of the angles of incidence and reflection of the X-rays, veryaccurate measurements of strain can be made by X-ray diffraction. Butthe slowness of the measurement and the complexity of the apparatus makethis more suitable for use as a reference technique than as a routineproduction metrology technique that needs to measure tens or hundreds ofwafers per day. Raman spectroscopy can measure semiconductor latticestrain because the shift of the Raman line depends on the strain of thesemiconductor (see, e.g., “Raman Microscopy”, G. Turrell and J. Corset(Eds.), pp. 275-277 (1996) Academic Press, ISBN 0-12-189690-0). Thiswill work only of the overlying films on the wafer do not interfere withthe Raman lines from the underlying material. The apparatus for Ramanspectroscopy is complex compared with that for shape measurement, andthe sensitivity and signal-to-noise ratio are poor because the Ramanlines in semiconductors are so weak relative to the incident laser line.For all of these reasons Raman is not suitable for routine productionmeasurements.

With respect to overlay metrology, extensive prior art can be founddescribing many different optical, algorithm and mark architectureswhich are relied on for this purpose. The current state of the art is,for example, the KLA-Tencor Archer 100 overlay metrology tool, whichoperates on the principle of high resolution bright field imaging ofeither box-in-box or periodic (AIM) two-layer metrology structures. Witha box-in-box structure, the displacement between the centers of symmetryof two or more features, sequentially generated in a number ofpatterning steps is calculated by image processing of images acquiredthrough a microscope and stored digitally. This technique furtherdescribed and analyzed by Neal T. Sullivan, “Semiconductor PatternOverlay”, in Handbook of Critical Dimensions Metrology and ProcessControl, pp. 160-188, vol. CR52, SPIE Press (1993). Variations on suchbox-in-box structures are also described in U.S. Pat. Nos. 6,118,185 and6,130,750, the disclosures of both of which are incorporated herein byreference.

A known alternative to the box-in-box technique is known asscatterometry overlay. In this technique, information is extracted fromthe intensity of light reflected from a periodic overlay mark. Theoverlay mark consists of gratings printed over gratings in subsequentpatterning steps. In this approach, several overlay cells, withdifferent intentional offsets between the two gratings of each cell, areformed in close proximity. The difference between the intensities oflight scattered from these overlay marks allows a model-freedetermination of the overlay error. Such grating style targets(sometimes referred to as “AIM” marks) can be denser and more robust,than “box” or ring-type marks resulting in the collection of moreprocess information, as well as target structures that can betterwithstand the rigors of CMP. The use of such marks is described, e.g.,by Adel et al in commonly assigned U.S. Pat. Nos. 6,023,338, 6,921,916and 6,985,618, all three of which are incorporated herein by referencefor all purposes.

As the depth of focus and overlay control required for the smallestdimensions printed on the wafer shrink, simply controlling global waferstress below some threshold is no longer sufficient. In particular, therapid thermal annealing (sometimes referred to as spike anneal) neededto anneal semiconductor wafers after certain implant process steps hasto heat and cool the wafer very rapidly in order to minimize the timespent at high temperatures to limit diffusion of implanted atoms. Thisfast heating and cooling subjects the wafer to significant stresses asdifferent parts of the wafer heat and cool at different rates. Some ofthese stresses may remain “frozen in” after the wafer has cooled. Laserspike anneal uses a laser to rapidly heat the wafer in an attempt toachieve very high surface temperatures in a very short time. However,the laser is typically not powerful enough to heat the whole surfacesimultaneously. Instead, sections or strips are annealed one at a timeeventually covering the whole wafer surface. Because only a part of thewafer is at high temperature at any one time, very high stresses can begenerated and some of these stresses remain after processing.Non-uniform stresses in a wafer can distort the local shape of the waferin complex ways. For example, the wafer may bend both in-plane and outof plane as a result of non-uniform stresses.

The manufacture of modern integrated circuit chips requires very manydifferent patterns to be layered one on another. Each new pattern has tobe accurately registered with patterns already on the chip. Thepatterning tool (e.g., a scanner or stepper) that prints the pattern onthe wafer contains subsystems that measure the location, height and tiltof the existing pattern. The time available to make these measurementsis limited because these measurements have to be done while the previouswafer is being exposed (or otherwise processed). Consequently, thenumber of measurements that can be made during such time is limited.

If the stress changes between one patterning step and the next, theshape of the wafer in X, Y and Z can change. If the change in stress isuniform then the shape changes can generally be represented accuratelyenough as linear distortions of the shape. In such a case, themeasurements made by the patterning tool are often sufficiently accurateto correct for the distortions. However, if the changes in stress arenon-uniform then the shape changes are complex and linear models may notbe accurate enough.

Prior art lithography tools may attempt to make the wafer as flat aspossible by using a vacuum chuck to suck the wafer down onto a veryprecisely machined flat surface. Typically, in order to minimize contactbetween the wafer backside and the chuck surface, the chuck uses a largenumber of pins to support the wafer. Because of the vacuum, acombination of atmospheric pressure and gravity forces the wafer downonto the pins and also causes some sag of the wafer between the pins,which are, by design, closely spaced to minimize the sag. The stressesin the wafer, the atmospheric pressure and force of gravity on the waferand forces of the pins on the wafer where the wafer contacts a pin allinteract to determine the shape of the wafer.

Wafer defocus of 50 nm may cause overlay shifts of approximately 10 nm.According to the 2005 ITRS roadmap, at the 32-nm node, the overallbudget for overlay accuracy on critical layers is expected to beapproximately 5.7 nm 3σ. A fraction of this amount (perhaps 50%) can beallocated to overlay caused by defocus. Based on these numbers, no morethan about 15 nm of defocus could be tolerated at the 32-nm node.Without dynamic adjustment of focus and/or overlay, the wafer would berequired to be flat to within to within ±15 nm within the area of thedie in order to keep overlay registration within the required limits.Scanners do adjust the leveling of each individual die before printing,but the leveling only corrects for average slopes in the X and Ydirections (e.g., a tilted wafer plane) and not for vertical distortionson scale lengths shorter than a die.

The complex distortions of the shape of the wafer in X, Y and possibly Zon the chuck due to the non-uniform changes in stress are not adequatelyaccounted for by the patterning tool leading to regions of the waferwhere yield is low due to poor alignment of one pattern with earlierpatterns on chips in that area of the wafer.

It is within this context that embodiments of the present inventionarise.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and advantages of the invention will become apparent uponreading the following detailed description and upon reference to theaccompanying drawings in which:

FIG. 1 is a block diagram of a semiconductor wafer processing systemaccording to an embodiment of the present invention.

FIG. 2 is a flow diagram illustrating a method of process control insemiconductor wafer processing according to an embodiment of the presentinvention.

FIG. 3 is a flow diagram illustrating a method of process control insemiconductor wafer processing according to an alternative embodiment ofthe present invention.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS

Although the following detailed description contains many specificdetails for the purposes of illustration, anyone of ordinary skill inthe art will appreciate that many variations and alterations to thefollowing details are within the scope of the invention. Accordingly,the exemplary embodiments of the invention described below are set forthwithout any loss of generality to, and without imposing limitationsupon, the claimed invention.

Embodiments of the present invention include a method and apparatus forprocess control in a lithographic process are described. Metrology maybe performed on a substrate either before or after performing alithographic patterning process on the substrate. One or morecorrectables to the lithographic patterning process may be generatedbased on the metrology. The lithographic patterning process performed onthe substrate (or a subsequent substrate) may be adjusted with thecorrectables.

Embodiments of the present invention utilize various methods of stress,topography (shape) and overlay metrology in both feed-forward andfeedback control loops with patterning, deposition and thermalprocessing tools in order to enhance die yield in semiconductor devicemanufacture. By automatically adjusting the patterning step tocompensate for variations in prior processing steps, the maximum yieldmay be obtained from each wafer even when the stress from a givenprocess changes over time or is non-uniform across the wafer. Unlike theprior art, embodiments of the present invention utilize direct feedbackor feed forward of high order wafer and field level stress or topographymetrology data as a means of controlling patterning, deposition andthermal processing tools. The prior art, by contrast, relied on keepinga global (or wafer average) stress introduced at each process step belowsome (process-specific) predetermined control limit in order to maintainthe overall stress level. Just measuring a global or average stressvalue cannot reliably catch all local deviations in stress since a largestress in a small area may have only a small effect on the globalstress, or large positive and negative local stresses in different areasmay partially cancel each other out leading to low average stress.Furthermore since the distortions at any location on the wafer are theresult of the net effect of all the prior processing steps, tightcontrol limits may need to be imposed on each individual step to avoidcumulative effects at some wafer location causing unacceptabledistortions. Imposing a low global stress control limit on a processstep in order to avoid stress accumulating over multiple steps as wellas to ensure a reduced probability of local stress exceeding somethreshold may result in a more expensive and less efficientmanufacturing process. Low control limits may require frequentadjustments to the process tools in order to keep them within that limitresulting in a less time available on the process tool for processingwafers and hence low productivity or the a need to purchase moreprocesses tools than otherwise necessary to compensate for the reducedproductivity.

FIG. 1 illustrates an apparatus 100 that according to an embodiment ofthe present invention. The apparatus 100 includes one or moresemiconductor processing tools 104, 120, a metrology tool 110 and acontroller 130. Two or more of the processing tools 104, 120 andmetrology tool 110 may reside in a common chamber 106. Substrates 101undergo fabrication-related processing in the processing tools 104, 120.The substrates may be transferred among the processing tools 104, 120and metrology tool 110, e.g., using wafer handling robots or automatedmaterials handling system or some combination of both. By way ofexample, the substrates may be semiconductor wafers or reticles. As usedherein, a reticle refers to a mask (also known as a photomask) used inphotolithography. The metrology tool 110 analyzes the substrates 101before and/or after such processing. The controller 130 may useinformation from the processing tools 104, 120 and metrology tool 110 toprovide feedback or feed-forward control of the processing tools. Theprocessing tools 104, 120, metrology tool 110 and controller 130 maycommunicate with each other through a data bus 102.

By way of example, and without limitation of embodiments of theinvention, the metrology tool 110 may include an overlay tool, a thinfilm tool, such as a spectroscopic ellipsometer, an electron beam toolsuch as a critical dimension scanning electron microscope (CD-SEM), orscatterometry tool. By way of example, and without loss of generality,the metrology tool 110 may be a thin film metrology tool. Examples ofsuch tools include optical thin film metrology tools, such asellipsometer-, scatterometer- and interferometer-based tools.Alternatively, the metrology tool 110 may be based on electric sensorssuch as capacitive sensors that can measure variations in substrateheight. By way of example, and without loss of generality, the metrologytool may be an optical thin film metrology system based on spectroscopicellipsometry. An example of such a tool is a Spectra Fx 200 optical thinfilm metrology system from KLA-Tencor Corporation of San Jose, Calif.Such systems generally include a focus sensor that may be used tomeasure changes in the shape of a substrate 101 due to processesoccurring in the processing tools 104, 120.

The processing tools 104, 120 generally include a lithographicpatterning tool 120 such as a scanner or stepper developer. Suchdevelopers are similar in operation to a slide projector or aphotographic enlarger. Such tools are often used in photolithographicprocesses used to form microscopic circuit elements on the surface of asemiconductor wafer. In the pattering tool, the substrate is retained ona stage 121, which may include a chuck, e.g., a vacuum chuck or anelectrostatic chuck. Elements of a circuit or other component to becreated on the IC are reproduced in a pattern of transparent and opaqueareas on the surface of a photomask or reticle 126. The pattern on thereticle 126 often corresponds to a pattern for a single die or chip.Light from a source 122 passes through the reticle 126, forming an imageof the reticle pattern. The image is focused and reduced by a lens 128,and projected onto the surface of a substrate 101 that is coated with aphotoresist 103. The focused image on the resist 103 is often referredto as an exposure field 105. After exposure, the coated substrate 101may be chemically developed, causing the photoresist 103 to dissolve incertain areas according to the amount of light the areas received duringexposure. This transfers the pattern on the reticle 126 to the resist103. The patterning tool 120 may be equipped with heater elements 125,such as heat lamps, to facilitate heating of the resist 103 eitherbefore or after exposure, e.g., to harden it. The patterning tool 120may be a stepper with an alignment system 123 that moves the substrate101 after exposing one die so that another portion of the substrate 101may be exposed with the same exposure field 103. The patterning tool 120may also be configured as a scanner. Scanners are steppers that increasethe length of the exposure field 103 by moving the reticle 126 and stage121 in opposite directions to each other during the exposure. Instead ofexposing the entire field at once, the exposure is made through an“exposure slit” 124 that is as wide as the exposure field 105, but onlya fraction of its length (e.g., a 9×25 mm slit for a 35×25 mm field).The image from the exposure slit 124 is scanned across the exposure areaon the substrate 101.

The substrate 101 with the developed resist 103 may then be subject tofurther processing, e.g., etching or deposition. Such processes may takeplace in other processing tools 104. Such tools may includespin-coaters, which deposit the resist on the substrate 101 or pre-bakechambers, in which the resist is heated prior to exposure or developingin the patterning tool 120. In addition, the other tool 104 may includea deposition tool, an etch tool, an ion implant tool, a resistapplication tool, a resist stripping tool, or a chemical mechanicalplanarization (CMP) tool. The substrate 101 may then be cleaned,recoated with photoresist, then passed through the patterning tool 120again in a process that creates the circuit on the substrate 101 layerby layer.

The controller 130 may include a central processor unit (CPU) 131 and amemory 132 (e.g., RAM, DRAM, ROM, and the like). The CPU 131 may executea process-control program 133, portions of which may be stored in thememory 132. The memory may contain data 136 related to processesoccurring in the tools 104, 120 and/or metrology performed by themetrology tool 110 on one or more substrates 101. The controller 130 mayalso include well-known support circuits 140, such as input/output (I/O)circuits 141, power supplies (P/S) 142, a clock (CLK) 143 and cache 144.The controller 130 may optionally include a mass storage device 134 suchas a disk drive, CD-ROM drive, tape drive, or the like to store programsand/or data. The controller 130 may also optionally include a displayunit 137 and user interface unit 138 to facilitate interaction betweenthe controller 130 and a user. The display unit 137 may be in the formof a cathode ray tube (CRT) or flat panel screen that displays text,numerals, or graphical symbols. The user interface 138 may include akeyboard, mouse, joystick, light pen or other device. The precedingcomponents may exchange signals with each other via an internal systembus 150. The controller 130 may be a general purpose computer thatbecomes a special purpose computer when running code that implementsembodiments of the present invention as described herein.

By way of example, the program 133 may implement a process control loopin which stress and/or shape and/or overlay metrology data, acquired ata high spatial density across the substrate 101 is used to calculatecorrections to the process taking place in the tools 104, 120 by variousmodeling methods. Such corrections may subsequently be used to implementhigh order overlay and focus corrections to the patterning process. Inthis way, the patterning process is enabled as a tool to compensate fordeformations induced in process steps prior to patterning. This isdifferent from the existing state of the art, since in currentpatterning tools, there are severe constraints on the time available toperform metrology activities on the wafer in preparation for thepatterning step. Due to these time constraints, in situ-metrology doesnot currently perform high density sampling of stress and deformationmetrology, in order to enable high order focus and overlay compensationduring the subsequent patterning step.

As illustrated in FIG. 2, the program 133 may implement a method 200 forprocess control in a lithographic process. In FIG. 2, vertical dashedarrows indicate flow of wafers, horizontal dashed arrows indicate flowof data, and solid arrows indicate flow of substrates 101. According tothe method 200, substrates 101 transition from the processing tool 104,which may induce stress or deformation into the metrology tool 110. Byway of example, a heating process, such as rapid thermal processing(RTP) may optionally take place in the processing tool 104 as indicatedat 202. Stress and deformation metrology may then be performed in themetrology tool 110, as indicated at 204. Specifically, the metrologytool may measure the topography (e.g., thickness) of or stress at one ormore locations in one or more layers of material (e.g., thin films)formed on the substrate 101. Metrology data 201 obtained at 204 may beused as input for a modeling module 210, which may be implemented aspart of the program 133. Alternatively, the modeling module 210 may beimplemented wholly or partly in hardware. By way of example, themodeling module 210 may perform finite element chucking deformationanalysis 212, which calculates the predicted shape deformation (in threedimensions) of the wafer when chucked on the stage 121 of the patterningtool 120. The chucking deformation analysis 212 may be based onmetrology data measuring the deformation of a test substrate that issufficiently similar to the substrate 101. The test substrate mayundergo processing in the patterning tool 120 with a test pattern on thereticle 126 while the test substrate is chucked to the stage 121. Themetrology tool 110 may then obtain deformation data on the testsubstrate. In addition, the modeling module 210 may perform a simulationof the impact of this deformation on the pattern generated during asubsequent patterning step in the patterning tool 120. The impact of thedeformation on the pattern may be in the form of a through-focus patternplacement prediction 214, which may be determined based on knowncharacteristics of the patterning process such as lithography systemfield dependent non-telecentric imaging.

Deformation data may then be input to a correctables generation engine205, which may be implemented as part of the program 133. Alternatively,the correctables generation engine 205 may be implemented wholly orpartly in hardware. The correctables generation engine 205 may convertthe results of the modeling module 210 to the coordinate system of thepatterning tool 120. The correctables generation engine 205 may alsotake as input, overlay, dose and focus data, as well as feedback frommetrology data from previous substrates 101 or previous substrate lots.The correctables generation engine 205 may also receive relevant contextdata 203 such as substrate-ID lot-ID, substrate-ID, layer-ID, tool-ID,chamber-ID, or chuck-ID in real time. The context data 203 may be highlyuseful for the correctables generation engine 205 since these variouscontext keys may all impact the processing taking place in thepatterning tool. The substrate 101 is then patterned, as indicated at206, after high order wafer and field level corrections have beenapplied, e.g., to overlay and/or focus patterning system controls withinthe patterning tool 120. The patterning process at 206 may includeexposure of the resist 103 followed by baking to harden the resist. Byway of example, the patterning tool 120 may be characterized by a numberof parameters between the reticle. The correctables generation engine205 may feed forward adjustments to one or more of these parameters tothe patterning tool 120 as correctables 207. By way of example, andwithout limitation, the correctables 207 may include adjustments to anyof the parameters used in computing an amount of overlay error dx, dy inthe x and y directions at a location Xf, Yf within a field having acenter at 0,0. The relevant parameters may differ depending on thepatterning tool 120 and computational method used. For a scanner tool, amethod referred to as an X and Y method, may be used to compute thequantities dx and dy as follows:

dx=FieldOffsetX+(FieldMagX×Xf)+(FieldRotX×−Yf)

dy=FieldOffsetY+(FieldMagY×Yf)+(FieldRotY×Xf), where:

FieldOffsetX and FieldOffsetY refer to field offsets in the x and ydirections;FieldMagX and FieldMagY refer to field magnifications in the x and ydirections; andFieldRotX and FieldRotY refer to field rotations with respect to the xand y directions;

For scanner tool, an alternative method, referred to as asymmetrical/asymmetrical method, may be used to compute dx and dy by:

dx=FieldOffsetX+(FieldMag×Xf)+(FieldRot×−Yf)+(AsymFieldMag×Xf)+(AsymFieldRot×−Yf);and

dy=FieldOffsetY+(FieldMag×Yf)+(FieldRot×Xf)+(AsymFieldMag×−Yf)+(AsymFieldRot×−Xf),

where AsymFieldMag refers to an asymmetrical field magnification andAsymFieldRot refers to an asymmetrical field rotation.

For a stepper tool, dx and dy may be computed as:

dx=FieldOffsetX+(FieldMag×Xf)+(FieldRot×−Yf); and

dy=FieldOffsetY+(FieldMag×Yf)+(FieldRot×Xf).

Specifically, the correctables 207 may include adjustments toFieldOffsetX, FieldOffsetY, Field MagX, FieldMagY, FieldRotX, FieldRotY,AsymFieldMag and AsymFieldRot.

After patterning, overlay focus the substrate 101 may be sent to themetrology tool 110 (or a different metrology tool) where post patterningmetrology (e.g., dose and/or overlay metrology) may be performed on thesubstrate 101 as indicated at 208. Post patterning metrology data 209may be used to provide feedback to the patterning tool 120 forpatterning of a subsequent substrate or lot. For example, the postpatterning metrology data 209 may be input to the modeling module 210which may apply substrate level overlay analysis 216 and/or field leveloverlay analysis 218 to the post patterning metrology data 209. Theresults of such analysis may then be fed back to the correctablesgeneration engine 205.

In embodiments of the present invention, the metrology tool 110 maymeasure wafer stress and/or topography at critical process steps withmore detail (spatial resolution) than is current practice. As discussedabove, the typical prior art practice is only to monitor a wafer averagestress. In embodiments of the present invention, by contrast, waferstress may be monitored at a resolution of one, or a few, mm (e.g.,about one millimeter to about five millimeters) as required to make anaccurate prediction of the interaction with the chuck. These moredetailed measurements are combined with models of how these stresses orshape changes interact with the patterning tool wafer chuck in order tofeed high-order correctables 207 to the patterning tool 120. As aresult, the patterning tool can make real-time adjustments duringscanning in order to produce better registration between the printedpattern and prior patterns on the substrate 101. No such modeling orfeed-forward scheme is used in prior art wafer processing systems.

Any suitable technique for measuring substrate stress or substrate shapemay be used at 204 and/or 208 as long as the technique is adapted toprovide sufficiently high spatial resolution. Any of the prior arttechniques for measuring overlay error may be used. Critical dimension(CD) measurements may be used in conjunction with the overlaymeasurements in order to measure how much focus has changed. Thecorrectables generation engine 205 may generate the correctables 207based on a theoretical model of how the wafer stress and/or shapeinteract with the chuck or may be based entirely on empiricalcorrelations between overlay measurements and stress/shape measurementsor on a combination of the two. The model may be created once for aspecific patterning tool 120, or the correctables engine 205 and/ormodeling module 210 may constantly and automatically update the model aspost pattering overlay measurement results 209 are accumulated.

In embodiments of the present invention, some or all of the substrates101 processed by the patterning tool 120 may be measured by themetrology tool 110. For example, 100% of the substrates 101 may bemeasured for stress and/or shape after a critical processing step and100% of the substrates may be measured for overlay errors afterpatterning. Alternatively, only selected subsets of the substrates 101may be measured by the metrology tool 110 both before and afterpatterning. If a single process tool (or single process chamber on aspecific tool) has a repeatable signature of substrate distortion, itmay be sufficient to measure one substrate per lot from that tool (orchamber) or one wafer per several lots for either the stress and/orshape or the overlay measurement (or both). In some cases, a tool mayhave more than one chuck and each chuck may have a different signature.The signature, e.g., measurements taken on substrates processed with theparticular tool, chamber, chuck, etc. (or modeling analysis based onthese measurements) may be stored in the memory 132. The signature maybe retrieved and selectively fed into the correctables generation engine205 based on context data 203, such as a tool-ID or chamber-IDassociated with the substrate 101.

As illustrated in FIG. 3, the program 133 may implement an alternativemethod 300 for process control in a lithographic process. In FIG. 3,vertical dashed arrows indicate flow of wafers, horizontal dashed arrowsindicate flow of data, and solid arrows indicate flow of substrates 101.According to the method 300, substrates 101 transition to the metrologytool 110 from a previous lithographic process 302. The previouslithographic process 302 may involve any lithographic step, e.g., resistapplication, resist exposure, resist developing, resist stripping, rapidthermal processing, material deposition, etching, thermal oxidation, ionimplantation, and the like. Stress and/or topography metrology may thenbe performed in the metrology tool 110, as indicated at 304.Specifically, the metrology tool 110 may measure the topography (e.g.,thickness) of or stress at one or more locations in one or more layersof material (e.g., thin films) formed on the substrate 101. Metrologydata 301 may be analyzed at 306 to obtain information about film stressor topography of the substrate 101.

After metrology at 304, the substrate 101 is sent to the lithographicpatterning tool 120, e.g., for resist exposure and or developing. Afterprocessing with the patterning tool 120, the substrate 101 may be sentto the metrology tool 110 (or a different metrology tool) for postprocessing metrology 308. Such post processing metrology may includeoverlay metrology, critical dimension (CD) metrology, focus metrology orsome combination of two or more of these.

Information collected at 306 may provide feed forward to a scannercorrectables generation engine 305, which may be implemented as part ofthe program 133. Alternatively, the scanner correctables generationengine 305 may be implemented wholly or partly in hardware. The scannercorrectables generation engine 305 may convert metrology informationcollected at 306 to the coordinate system of the patterning tool 120.The correctables generation engine 305 may also take as input, overlay,dose and focus data, as well as feedback information collected at 310from post-processing metrology data 309 from the post-processingmetrology 308. The correctables generation engine 305 may also receiverelevant context data 303 such as substrate-ID lot-ID, substrate-ID,layer-ID, tool-ID, chamber-ID, reference tool-ID, reticle-ID,pre-tool-ID, chuck-ID, and the like in real time. The context data 303may be highly useful for the correctables generation engine 205 sincethese various context keys may all impact the processing taking place inthe patterning tool 120. The correctables generation engine 305 may feedforward adjustments to one or more patterning tool parameters to thepatterning tool 120 as scanner correctables 307.

Various Methods are available for generating the scanner correctables307. For example feed-forward information collected at 306 may be usedto generate high-order grid correction, individual linear and/orhigh-order field-level corrections, focus corrections and the like.Feed-forward information collected at 306 may cover substrateshape-related overlay error. Such errors are often process related andmay depend on the nature of the previous lithographic process 302, e.g.,whether the previous process is a thermal process, etch process, CMPprocess . . . etc. In addition, feedback information collected at 310may be used to generate high-order grid corrections, linear and/orhigh-order average of fields correction, linear and/or high-orderindividual field level corrections and the like.

The feedback information collected at 310 may cover exposure toolsignatures such as stage, scanning, reticle stage, lens and illuminationsignatures, reticle signature, exposure tool matching signature, andremaining process related signatures.

Embodiments of the present invention can reduce patterning errors andimprove yield for processes that require high precision and small designrules.

While the above is a complete description of the preferred embodiment ofthe present invention, it is possible to use various alternatives,modifications and equivalents. Therefore, the scope of the presentinvention should be determined not with reference to the abovedescription but should, instead, be determined with reference to theappended claims, along with their full scope of equivalents. Anyfeature, whether preferred or not, may be combined with any otherfeature, whether preferred or not. In the claims that follow, theindefinite article “A”, or “An” refers to a quantity of one or more ofthe item following the article, except where expressly stated otherwise.The appended claims are not to be interpreted as includingmeans-plus-function limitations, unless such a limitation is explicitlyrecited in a given claim using the phrase “means for.”

1. A method for process control in patterning a substrate, comprising:a) performing metrology on the substrate either before or afterperforming a patterning process on the substrate; b) generating one ormore correctables to the patterning process based on the metrologyperformed in a); and either c) adjusting the patterning processperformed on the substrate with the correctables, if the metrology isperformed before the patterning process; or d) adjusting the patterningprocess performed on a subsequent substrate with the correctables, ifthe metrology is performed after the patterning process; or e) both c)and d).
 2. The method of claim 1, wherein patterning process performedon the substrate with the correctables the metrology is performed beforethe patterning process and generating the one or more correctablesincludes performing an analysis of deformation of the substrate.
 3. Themethod of claim 2, wherein adjusting the patterning process performed onthe substrate with the correctables includes feeding the correctablesforward to a patterning tool, adjusting one or more parameters of thepatterning tool using the correctables and performing the patterningprocess on the substrate with the patterning tool.
 4. The method ofclaim 2, wherein the correctables include adjustments to a field offset,a field magnification, or a field rotation of a lithographic patterningtool.
 5. The method of claim 4 wherein the field magnification is anasymmetric field magnification.
 6. The method of claim 4 wherein thefield rotation is an asymmetric field rotation.
 7. The method of claim 2wherein performing an analysis of deformation of the substrate includesperforming a through focus pattern placement prediction.
 8. The methodof claim 2 wherein performing metrology includes performing stressand/or topography metrology for one or more layers of material on thesubstrate.
 9. The method of claim 2 wherein performing an analysis ofdeformation of the substrate includes predicting shape deformation (inthree dimensions) of the substrate when chucked on a stage of apatterning tool.
 10. The method of claim 2 wherein performing ananalysis of deformation of the substrate includes monitoring a localizedstress of the substrate at a plurality of locations.
 11. The method ofclaim 10 wherein monitoring a localized stress includes monitoring thelocalized stress at a spatial resolution of between about 1 mm and about5 mm.
 12. The method of claim 1 wherein a) includes performing stressand/or topography metrology before performing the patterning process.13. The method of claim 12 wherein a) includes performing overlay,critical dimension or focus metrology after performing the patterningprocess.
 14. The method of claim 1 wherein a) includes performing stressand/or topography metrology before performing the patterning process andafter a previous process.
 15. The method of claim 14 wherein a) includesperforming overlay, critical dimension or focus metrology afterperforming the patterning process.
 16. The method of claim 1 whereingenerating the one or more correctables includes the use of context dataassociated with the processing of the substrate.
 17. The method of claim16 wherein the context data includes a lot-ID, substrate-ID, layer-ID,tool-ID, chamber-ID, scanner-ID, or chuck-ID, reference tool-ID,reticle-ID or pre-tool-ID associated with processing of the substrate.18. The method of claim 1 wherein the patterning process comprises anexposure step, a bake step and a develop step.
 19. The method of claim 1wherein the metrology is performed after the patterning process.
 20. Themethod of claim 19 wherein performing metrology on the substrateincludes performing overlay, dose, or focus metrology on the substrate.21. The method of claim 20 wherein the correctables include adjustmentsto a field offset, a field magnification, or a field rotation of apatterning tool.
 22. The method of claim 21 wherein the fieldmagnification is an asymmetric field magnification.
 23. The method ofclaim 21 wherein the field rotation is an asymmetric field rotation. 24.The method of claim 20 wherein generating the one or more correctablesincludes performing an overlay analysis.
 25. The method of claim 24wherein the overlay analysis is a substrate level overlay analysis or afield level overlay analysis.
 26. The method of claim 1 whereingenerating the correctables includes modeling an interaction between thesubstrate and a chuck used to retain the substrate during the patterningprocess to obtain a shape of the substrate when retained by the chuck.27. The method of claim 26, further comprising converting the shape ofthe substrate when retained by the chuck to a coordinate system for apatterning tool used during the patterning process.
 28. An apparatus forprocess control in patterning a substrate, comprising: a metrology tooladapted to perform metrology on the substrate either before or afterperforming a patterning process on the substrate; and a controllercoupled to the metrology tool, wherein the controller is adapted togenerate one or more correctables to the patterning process based on themetrology and either: a) adjust the patterning process performed on thesubstrate with the correctables, if the metrology is performed beforethe patterning process; or b) adjust the patterning process performed ona subsequent substrate with the correctables, if the metrology isperformed after the patterning process; or c) both a) and b).
 29. TheApparatus of claim 28, wherein adjusting the patterning processperformed on the substrate with the correctables includes feeding thecorrectables forward to a patterning tool.
 30. The apparatus of claim 28wherein the metrology tool is a thin film metrology system.
 31. Theapparatus of claim 28 wherein the metrology system is an optical thinfilm metrology system.
 32. The apparatus of claim 28 wherein themetrology system includes an interferometer adapted to measure height ofone or more features on the substrate.
 33. The apparatus of claim 28wherein the metrology system includes one or more capacitive sensorsadapted to measure height of one or more features on the substrate. 34.The apparatus of claim 28 wherein the controller includes modelingmodule and a correctables generation module.
 35. The apparatus of claim34 wherein the modeling module is configured to model an interactionbetween the substrate and a chuck used to retain the substrate duringthe patterning process to obtain a shape of the substrate when retainedby the chuck.
 36. The apparatus of claim 35 wherein the modeling moduleis configured to model the interaction by a finite element chuckingdeformation analysis that calculates a predicted shape deformation ofthe wafer when retained by the chuck.
 37. The apparatus of claim 28wherein the controller includes a correctables generation moduleconfigured to generate corrections to one or more parameters of apatterning tool in response to metrology data obtained from themetrology tool.
 38. The apparatus of claim 37, further comprising, apatterning tool, wherein the patterning tool is coupled to thecontroller.